1. Field of the Invention
The present invention relates to a resist composition containing a novel acid generator, a method of forming a resist pattern using the resist composition, an acid generator for a resist composition or a novel compound useful as a precursor of the acid generator, and a method of producing the compound.
Priority is claimed on Japanese Patent Application No. 2009-107917, filed Apr. 27, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X ray.
As shortening of the wavelength of the exposure light source progresses, it is required to improve various lithography properties of the resist material, such as the sensitivity to the exposure light source and the resolution capable of reproducing patterns of minute dimensions. As a resist material which satisfies these conditions, a chemically amplified resist composition is known, which includes a base material component that exhibits a changed solubility in an alkali developing solution under the action of acid and an acid generator component that generates acid upon exposure.
Conventionally, resins have been used as the base material components within these types of chemically amplified resist compositions, and examples of these resins include polyhydroxystyrene (PHS), PHS-based resins in which a portion of the hydroxyl groups of a PHS have been protected with acid dissociable, dissolution inhibiting groups, copolymers derived from (meth)acrylate esters, and resins in which a portion of the carboxyl groups within these (meth)acrylate esters have been protected with acid dissociable, dissolution inhibiting groups (for example, refer to Patent Document 1). Here, the term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position.
As acid generators, various types have been proposed including, for example, onium salt-based acid generators; oxime sulfonate-based acid generators; diazomethane-based acid generators; nitrobenzylsulfonate-based acid generators; iminosulfonate-based acid generators; and disulfone-based acid generators. Of these, as an onium salt-based acid generator, iodonium salts containing iodonium ions as cations and sulfonium salts containing sulfonium ions as cations have conventionally been used. Further, as an anion (acid) that forms a salt with these cations, a perfluoroalkylsulfonic acid ion is generally used (for example, refer to Patent Document 2).
However, a perfluoroalkyl chain of 6 or more carbon atoms is hardly decomposable, and hence, in consideration of minimizing bioaccumulation to improve safety in handling, a perfluoroalkylsulfonic acid ion of no more than 4 carbon atoms such as a nonafluorobutanesulfonic acid ion or the like has been mainly used as the above-mentioned perfluoroalkylsulfonic acid ions.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2005-037888